Elsevier

Intermetallics

Volume 10, Issues 11–12, November 2002, Pages 1283-1288
Intermetallics

Mechanical properties of tungsten fiber reinforced ZrAlNiCuSi metallic glass matrix composite

https://doi.org/10.1016/S0966-9795(02)00136-XGet rights and content

Abstract

Tungsten fiber reinforced (Zr55Al10Ni5Cu30)98.5Si1.5 metallic glass composites were fabricated and characterized. The mechanical properties of the composite under compression and tension were investigated. Tungsten reinforcement greatly increased compressive strain to failure compared to the unreinforced (Zr55Al10Ni5Cu30)98.5Si1.5 metallic glass. The compressive failure mode changed from a single shear band to multiple shear bands and to localized fiber buckling and tilting as the volume fraction of tungsten fiber increased. The maximum tensile strength and strain to failure of each of the composites were lower than those of unreinforced material due to the lack of substantial shear bands. Tensile toughness changed to some extent due to different interface reactions. The reason for the improved mechanical properties is discussed.

Introduction

Bulk metallic glasses (BMGs) have excellent mechanical properties such as high yield strength and high elastic limit, roughly a 2% elastic strain limit in tension or compression [1]. They also have very good fracture toughness, for example, Zr41.25Ti13.75Cu12.5Ni10Be22.5 bulk metallic glass has a plane strain fracture toughness of about 20–55 MNm1/2 [2], [3], [4]. Unfortunately, upon yielding in tension or compression test, metallic glasses tend to form localized shear bands. The localization of shear is associated with the absence of strain hardening mechanism and thermal softening during adiabatic heating of the material. Therefore, without geometrical confinement, failure often occurs along a single band, which traverses the sample. In contrast to metallic glasses, useful crystalline metals exhibit substantial plastic strains following yielding under tension. This results in high fracture toughness, impact resistance, etc. A new and applicable material may be synthesized by combining the merits of both materials, namely, metallic glasses and crystalline metals, to form metallic glass matrix composites. It is the motivation of many researchers to explore fabrication of metallic glass composites.

It was found [5] that high density of multiple shear bands formed when the laminated composite was deformed under tensile loading (tensile axis parallel to the layers) and overall plastic tensile strain of the order of 10% could be achieved. This showed the possibility of enforcing shear band confinement under tension by “trapping” multiple shear bands between the ductile metal layers. A number of investigations on metallic glass composites have proved that they possessed significantly improved mechanical properties and high structural efficiency of BMGs [6], [7], [8]. Conner et al [8] studied Zr41.25Ti13.75Cu12.5Ni10Be22.5 bulk metallic glass as the matrix in continuous fiber composites reinforced with tungsten and 1080 steel wire. It was found that tungsten reinforcement increased compressive strain to failure by over 900% compared to unreinforced Zr41.25Ti13.75Cu12.5Ni10Be22.5. They concluded that the increase in compressive toughness came from the fibers restricting shear band propagation, promoting the generation of multiple shear bands and additional surface area. The failure of the composites in compression by the formation of localized shear bands is of practical interest. This mode is greatly desired in the design of W-base kinetic energy penetrators [1]. Inoue and Zhang [9] have found that bulk Zr55Al10Cu30Ni5 metallic glass has a large glass-forming ability and can be fabricated into a specimen 30 mm in diameter. Furthermore, we found that a certain amount of Si addition to the Zr55Al10Cu30Ni5 alloy can further increase the glass-forming ability [10]. Therefore it is possible to fabricate tungsten fiber reinforced ZrAlNiCuSi bulk metallic glass composite of a large size by using infiltration casting method. The W fiber was used for two reasons: it either has a high melting temperature and limited reaction with the matrix material, or it can increase substantially the density of reinforced composite. A high density of composite can greatly increase the dynamic energy in the dynamic deformation case.

The plastic strain to failure of tungsten fiber reinforced Zr–Al–Ni–Cu–Si in compressive experiments increased from almost zero for the unreinforced metallic glass to up to 13%, which was the result of multiple shear band formation. The decrease of strain to failure of tungsten fiber reinforced metallic glass in tension was due to the fact that no substantial shear band formation occurred.

Section snippets

Experimental procedure

Ingots of (Zr55Al10Ni5Cu30)98.5Si1.5 were made by combining metals (purity 99.8% or better) in an induction furnace under argon atmosphere. Tungsten fiber with a nominal diameter of 250 μm was straightened and cut to 80 mm in length. The tungsten fibers were cleaned in an ultrasonic bath of acetone, followed by ethanol. Composite samples 6 mm in diameter and 90 mm in length were fabricated with tungsten fiber volume fraction of 10, 20, 28, 40, 50, 60, and 70%, respectively. Samples were cast in

Results and discussions

The physical properties of individual components in the composite are shown in Table 1. Because of its high melting temperature, the microstructure of the tungsten is unaffected during processing. Fig. 1 shows X-ray diffraction patterns of the ZrAlNiCuSi matrix, the alloy reinforced with 10% tungsten and 28% tungsten respectively. The patterns of the composite show diffraction peaks from tungsten fiber superimposed on the broad diffuse scattering maxima from the amorphous phase. No other phases

Conclusions

A new beryllium-free tungsten fiber reinforced Zr-based metallic glass composite was fabricated and characterized. The mechanical properties under compression and tension were tested. Tungsten fibers/ZrAlNiCuSi bulk metallic glass composite exhibits a large plastic deformation under compression due to multiple shear band formation which results in a large increase in compressive strain to failure. The compressive failure mode for those tungsten fibers reinforced composites change from shear

Acknowledgements

This work was performed with the support of the National Development Project for Basic Scientific Research of China under grant number G2000067201.

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